This invention relates to refolding fan-folded webs into a stack and, in particular, to refolding fan-folded paper from a high speed printer.
In data processing and communication applications, high speed printers are used to print the rapidly generated output of data processing machines. The medium on which printing generally is performed is "fan-folded", that is elongated webs having transversely extending folds longitudinally spaced with alternate folds pointing in opposite directions. The web is taken into the printer from a stack within which it is tightly folded at the spaced folds. In the course of printing, the web is unfolded and a need exists to refold it along its folds in a zigzag manner and into a stack. The web may be a single sheet of paper or consist of several sheets of paper interspersed with carbons. It is not uncommon to print up to several sheets with carbons.
It should be noted that the output of a high speed printer is not necessarily continuous and constant. The printer may generate printout faster when printing short lines than long ones. When slewing (feeding paper without printing), the paper moves through the printer at an extremely high speed. Further, with some types of printers, paper is fed from the printer discretely and only after a line has been printed. No paper movement occurs during printing, that is, the printer's paper output is not continuous. Still other printers print continuously while the paper is moving.
Numerous machines have been designed to stack the fan-folded printout from high speed printers. Oftentimes, a pair of paper feed tractors engage edge perforations in the paper and are used to feed the paper from its incoming stack through the printing mechanism and then to the outgoing stack being formed in a storage chamber. In some instances use has been made of vacuum chambers to receive, contain or control the paper. Also, various complex designs of chutes and movable arms have been employed to stack the paper neatly without misfolding and without jamming the storage compartment or the printing and paper drive mechanisms. These prior art arrangements, however, have proved to be complex in design, expensive to construct and not capable of reliably stacking the fan-folded printout of high speed printers operating over a wide range of speeds and involving large volumes of paper. The prior art arrangements have been noticeably deficient in situations where some memory of the folds is lost during the printing operation. For example, heat and pressure in certain printing operations partially iron out the folds in the paper which can lead to misfolds.